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A P wave, or compressional wave, is a
seismic body wave that shakes the ground back and forth in the
same direction and the opposite direction as the direction the
wave is moving.
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Paleoseismicity refers to earthquakes
recorded geologically, most of them unknown from human
descriptions or seismograms. Geologic records of past
earthquakes can include faulted layers of sediment and rock,
injections of liquefied sand, landslides, abruptly raised or
lowered shorelines, and tsunami deposits.
USGS and
university geologists study the walls of a trench across a
recently discovered strand of the Seattle fault.
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When you step on the accelerator in the
car or put on the brakes, the car goes faster or slower. When it
is changing from one speed to another, it is accelerating
(faster) or decelerating (slower). This change from one speed,
or velocity, to another is called acceleration. During an
earthquake when the ground is shaking, it also experiences
acceleration. The peak acceleration is the largest acceleration
recorded by a particular station during an earthquake.
Acceleration, Velocity,
Displacement (Image courtesy of Charles Ammon, Penn State)
Kinemetrics FBA-23
accelerograph.
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Pedogenic means pertaining to processes
that add, transfer, transform, or remove soil constituents.
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g
g is the acceleration of gravity 9.8 (m/s2) or the
strength of the gravitational field (N/kg) (which it turns out
is equivalent). G is the proportionality constant 6.67x10-11
(N-m2/kg2) in Newton's law of gravity. On
the other hand, the force of gravity, or F = mg, at the surface
of the earth, or F = GMm/r^2 at a distance r from the center of
the earth (where r is greater than the radius of the earth).
When there is an earthquake, the forces caused by the shaking
can be measured as a percentage of gravity, or percent g.
Gravity
The attraction between two masses, such as the earth and an
object on its surface. Commonly referred to as the acceleration
of gravity. Changes in the gravity field can be used to infer
information about the structure of the earth's lithosphere and
upper mantle.
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The period is the time interval
required for one full cycle of a wave.
(Image courtesy of
ThinkQuest)
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Plate Tectonics is the theory supported
by a wide range of evidence that considers the earth's
crust and upper
mantle to be composed of several large, thin, relatively
rigid plates that move relative to one another. Slip on faults
that define the plate boundaries commonly results in
earthquakes. Several styles of faults bound the plates,
including
thrust faults along which plate material is subducted or
consumed in the mantle,
oceanic spreading ridges along which new crustal material is
produced, and
transform faults that accommodate horizontal slip (strike slip)
between adjoining plates.
From "This Dynamic Earth:
The Story of Plate Tectonics"
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The Pleistocene is the time period
between about 10,000 years before present and about 1,650,000
years before present. As a descriptive term applied to rocks or
faults, it marks the period of rock formation or the time of
most recent fault slip, respectively. Faults of Pleistocene age
may be considered active though their activity rates are
commonly lower than younger faults.
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A Poisson distribution is a probability distribution that
characterizes discrete events occurring independently of one
another in time.
(Image courtesy of Alexei
Sharov, Virginia Tech)
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